Multi-beam resonant planar slot array antenna



Jan- 9, 1968 A. E. RATKEVICH E AL 3,363,253

MULTI-BEAM RESONANT PLANAR SLOT ARRAY ANTENNA Filed Jan. 18,. 1965 4 Sheets-Sheet 1 I r i INVENTORS ADAM E. RATKEVICH JEAN-CLAUDE BENSIMON RONALD L., NAYLOR Jan. 9, 1968 A. E. RATKEVICH ET AL MULTIBEAM RESONANT PLAN/8R SLOT ARRAY ANTENNA 4 SheetsSheet 2 Filed Jan. 18, 1965 Fig. 3

INVENTORS ADAM E. RATKEVICH JEANCLAUDE BENSIMON RONALD L. NAYLOR Fig.

'Fig. 5

Jan, 9, 1968 A. E. RATKEVICH ET AL 3,363,253

MULTIBEAM RE'SONANT PLANAR SLOT ARRAY ANTENNA Filed Jan. 18, 1965 4 Sheets-Sheet 3 ADAM E. RAT KEVICH- JEAN-CLAUDE BENSIMON RONALD L. NAYLOR Jan. 9, 1968 H PLANE E PLANE A. E. RATKEVICH ET AL MULTI-BEAM RESONANT PLANAR SLOT ARRAY ANTENNA Filed Jan. 18, 1965 /VERTICAL/ 4 Sheets-Sheet 4 ANTENNA BEAM CHARACTERISTICS Slal iype IlI III I II 11 Feed lype II I II 11' Y Number of beams 2 2 4 4 4 E Plane angle range 2l9.5 ll.5tal9.5 2l9.5 l9.5 ll.5 'l'ol9.5 H Plane angle range 0 0 l9.5 ll.5lol9.5 ll.5lo l9.5 Wide spacing sinex 352.5) 59.57; ssrsx ssesx restriction on S Resonani line '7 n 3 n n 3- reslriciion on S Eh-{x9 "T 'T S'Z T Wide sp g P x P 7\ P515) P 2.s P525). reslriclion on P Resonant line p 3 3; restriclion on P p- 2 X9 P 2 lg P 2' P 2 X9 P 2 xg General E Plane beam angle formula: Slll 9 ail- (2ar4 beams) General H Plane beam angle formula: sln 9 (4 beams) Fig. l3

INVENTORS ADAM E. RATKEVICH JEAN'CLAUDE BENSlMON RONALD L. NAYLOR United States Patent 3,363,253 MULTI-BEAM RESONANT PLANAR SLOT ARRAY ANTENNA Adam E. Ratkevich, La Mesa, Jean-Claude Bensimon, Garden Grove, and Ronald L. Naylor, San Diego, Calif., ssiguors to The Ryan Aeronautical (10., San Diego,

alif.

Filed Jan. 18, 1965, Ser. No. 426,332 8 Claims. (Cl. 343771) The present invention relates to antennas and more specifically to a multi-beam resonant planar slot array antenna.

Present antennas capable of producing multiple beams usually involve multiple or special reflectors, or lenses and contain considerable structure which is susceptible to vibration and microphonics. The beams are often not symmetrical due to inconsistencies in construction tolerances and the structure is bulky. Travelling wave planar arrays have also been used, but these are usually limited to two beams of undesirably wide beamwidth and are not particularly efiicient. The tolerances of such an array are critical and complex multiple feeds are normally 'used, with isolators between feeds and terminating loads in the waveguides, resulting in excess weight and many structural parts.

critical, since the symmetrical single feed ensures equal gain, beamwidth and beam angle of all beams, with negligible beam angle change under varying frequency and temperature conditions.

Another object of this invention is to provide an antenna wherein the beam pattern and number of beams is determined by the specific slot spacing and waveguide spacing, all in the same basically simple, unitary antenna structure, with its single feed.

A further object of this invention is to provide an antenna which is particularly suitable for use as a continuous wave Doppler transmitting antenna.

In the drawings:

FIGURE 1 is a bottom plan view of a four beam antenna array;

FIGURE 2 is a side elevation view thereof;

FIGURE 3 is an enlarged sectional view taken on line 3-3 of FIGURE 1;

FIGURE 4 is a sectional View taken on line 44 of FIGURE 3;

FIGURE 5 is a sectional view taken on line 5-5 of FIGURE 4;

FIGURE 6 is a bottom plan view of a two beam slot array;

FIGURES 7, 8 and 9 illustrate different slot spacing "arrangements;

cal elements and portions throughout .the specification and throughout the views of the drawing.

3,363,253 Patented Jan. 9, I968 Basic antenna structure The antenna, indicated generally at 10 in FIGURES l and 2, comprises a plurality of spaced, parallel waveguide radiating elements 12 of equal length, which are joined by a waveguide feeder element 14 extending perpendicular to the radiating elements and secured to each at the center thereof. The specific designations 12A and 14A will be explained hereinafter. The feeder element 14 thus forms a spine with radiating elements spaced along its length and extending symmetrically on opposite sides. As illustrated, the radiating elements 12 are all secured to one face of a support plate 16 and the feeder element 14 is secured to the other face thereof. Support plate 16, extending in the plane of the array, provides great rigidity to the structure, but is not essential to the operation of the antenna. In instances where surrounding structure in a particular installation can be used for support, or the antenna is small and rigid enough to be self-supporting, the plate can be omitted. At the center of feeder element 14 and perpendicular to the plane of the array is a waveguide input 18, provided with a connecting flange 20, as commonly used in waveguide assemblies, for connection to associated microwave apparatus. The ends of radiating elements 12 are closed by cap plates 22 and the ends of feeder element 14 are similarly closed by cap plates 24. In the feeder element 14 at the base of input 18 is a tuning slug 26, illustrated as a cylindrical post, the function being well known in relation to a waveguide. T structure, as formed by said input and feeder element.

At each junction of the feeder element 14 with a radiating element 12, the two waveguide elements are coupled through a feeder slot 28 inclined to the longitudinal axis of the feeder element. The feeder slots 28 are alternately inclined in opposite directions so that adjacent radiating elements 12 are in opposite phase relation.

Slot arrangements Each radiating element 12 is provided with a plurality of radiating slots in the wall remote from feeder element 14, the slots being elongated along the length of the radiating element. In each instance the slots are spaced longitudinally along the radiating slement and arranged in pairs, the slots of each pair being staggered on opposite sides of the radiating element center line. The longitudinal spacing of the slots along the radiating element, or in the H plane of the antenna, and the lateral spacing between radiating elements in the E plane of the antenna determine the number of beams radiated and the beam angles with respect to vertical.

With reference to FIGURE 7, a radiating element designated 12A is illustrated fragmentarily with two pairs of slots, each pair comprising a slot 30 and a slot 32 to clarify description, all slots being similar in size. In this particular arrangement all of the slots'are spaced equally in the H plane at a spacing P, which is a specific value of the wavelength of signal to be handled, as will hereinafter be explained in detail. The slots 30 and 32 of each pair are excited in opposite phase in this arrangement, which will be referred to as Type I. The end slot is spaced one quarter Ag (wavelength in guide) from the cap plate 22, which is the case in each slot configuration.

In FIGURE 8, the radiating element 12B has two pairs of slots 30'and 32 in which the slots of each pair are spaced apart a distance of one third P, while the distance from a point in one pair to the corresponding point in the next pair is equal to P. In this arrangement, which will be referred to as Type II, the slots 30 and 32 of each pair are of the same phase relation, but the adjacent pairs are of opposite phase.

The arrangement illustrated in FIGURE 9 shows the slots all equally spaced at a distance of one half Ag and are all in phase. This arrangement Will be referred to as Type III.

The spacing between the radiating elements 12 is also important, the configuration of FIGURE 10 showing the elements spaced at an equal distance S, between centers, along the feeder element 14A. This particular spacing in the E plane will be designated feeder Type IV.

Another spacing arrangement illustrated in FIGURE 11 and referred to as feeder Type V, has the radiating elements in pairs along feeder element 14B, with a spacing of one third S between centers of each pair and a spacing S between a point in one pair and a corresponding point in the next adjacent pair.

The different slot types and feeder types can be used in various combinations to provide different beam characteristics, as will be evident from the table of FIGURE 13. This table shows the values of P and S in terms of wavelength, the maximum spacings being indicated for each antenna configuration.

The antenna illustrated in FIGURE 1, for example, uses radiating elements 12A with slot Type II on a Type IV feeder element 14A. From the table it can be seen that this combination produces four beams, with a beam angle from vertical on the order of 19.5 degrees in the E plane and between 11.5 and 19.5 degrees in the H plane. The exact beam angles will depend on the specific dimensions of S and P, according to the formulas given in the table. The spacing of S is limited to a maximum of 1.5 times the wavelength A, while the spacing of P is limited to a maximum of 2.5 times the wavelength. To achieve the optimum waveguide resonance characteristics the S dimension should be where n is the number of half cycle variations in the field across the small cross sectional dimension of the waveguide, and Ag is the wavelength in guide. Also, to achieve proper resonance, the P dimension should be As a further example, a two beam antenna 34 is illus-' trated in FIGURE 6, which uses radiating elements 12C with Type III slots and Type IV feeder 14A. From the table it can be determined that the dimension S for this configuration is limited to a maximum of 1.5 times the wavelength, while P is limited to a maximum dimension of one wavelength. The appropriate resonant line restrictions are also indicated. With only two beams there is no beam angle in the H plane, the beam angle in the E plane being on the order of 19.5 degrees, depending on the specific S dimension.

By means of the standing wave slot excitation and paired slots with relatively wide spacing, the planar array is capable of producing two or four beams using a single inputlt will be seen that the Type III slots at half wave spacing and all in phase provide two beams, while the otherslot arrangements with oppositely phased slots provide four beams. The slot spacings are limited to prevent the two or four 'beam platterns from breaking up into four beams and eight or sixteen beams, respectively. In the case of the Type II slots and Type V feeder, the dis tinct pair arrangement causes a primary pattern nulling which allows the beam angle to be reduced to 11.5 de- 4 grees. 'As a comparison, travelling wave arrays capable of producing electrically tilted beams usually have a beam angle of well over degrees.

The single central input and symmetrical feed of the 5 antenna ensure symmetrical beams, each beam being related to the full antenna aperture. This makes possible narrow beam angles with a small antenna. There is negligible beam angle change with changes in frequency, or from temperature changes affecting the dimensions of the antenna. The latter is a result of the symmetrical feed, since any dimensional errors will affect each beam equally, the gain and beamwidth of all beams remaining equal. Due to the mechanical rigidity of the simple and light structure, the antenna is not susceptible to micro phonics caused by vibration. The antenna is particularly suitable for use with continuous Wave Doppler radar, such as used to determine and control the attitude of a hovering aircraft, or other vehicle, by comparison of the multiple beam signals. However, the use is not necessarily limited to this purpose. a

It is understood that minor variation from the form of the invention disclosed herein may be made without departure from the spirit and scope of the invention, and that the specification and drawings are to be considered as merely illustrative rather than limiting.

We claim:

1. A multiple beam planar slot array antenna, comprising:

an elongated waveguide feeder element having a microwave input;

a plurality of waveguide radiating elements fixed to and spaced along said feeder element, said radiating eiements being normal to and extending on opposite sides of said feeder element;

said feeder element having a slot communicating with each of said radiating elements;

each of said radiating elements having a plurality of longitudinally spaced pairs of slots.

2. A multiple beam planar slot array antenna, comprising:

an elongated waveguide feeder element having a microwave input;

a plurality of waveguide radiating elements fixed to and spaced along said feeder element, said radiating elements being normal to and extending on opposite sides of said feeder element;

said feeder element having a slot communicating with each of said radiating elements; 7

each of said radiating elements having a plurality of longitudinally spaced pairs of slots;

the slots of each pair being longitudinally spaced and staggered on opposite sides of the axis of the radiating element.

3. An antenna according to claim 2, wherein the spacing between said pairs of slots is greater than the spacing between the slots of each pair.

4. An antenna according to claim 2, wherein the spacing between said pairs of slots is a maximum of two and one-half times the Wavelength of the antenna.

5. An antenna according to claim 2, wherein the spacing between said radiating elements is a maximum of two and one-half times the wavelength of the antenna.

6. An antenna according to claim 2, wherein said radiating elements are arranged in pairs, the spacing be.- 'tween the elements of each pair being less than the. spacing between adjacent pairs.

7. A multiple beam planar slot array antenna, comprising:

an elongated waveguide feeder element having a single central microwave input;

a plurality of elongated waveguide radiating elements fixed to and spaced along a common face of said feeder element, said radiating elements being normal to and extending on opposite sides of said feeder 7 element;

said feeder element having a slot communicating with each of said radiating elements; each of said radiating elements having a plurality of longitudinally spaced pairs of radiating slots in the face thereof remote from said feeder element. 8. An antenna according to claim 7, wherein said radiating elements extend equally on opposite sides of said feeder element and said radiating slots are disposed symmetrically with respect to said input.

No references cited.

ELI LIEBERMAN, Primary Examiner. 

1. A MULTIPLE BEAM PLANAR SLOT ARRAY ANTENNA, COMPRISING: AN ELONGATED WAVEGUIDE FEEDER ELEMENT HAVING A MICROWAVE INPUT; A PLURALITY OF WAVEGUIDE RADIATING ELEMENTS FIXED TO AND SPACED ALONG SAID FEEDER ELEMENT, SAID RADIATING ELEMENTS BEING NORMAL TO AND EXTENDING ON OPPOSITE SIDES OF SAID FEEDER ELEMENT; SAID FEEDER ELEMENT HAVING A SLOT COMMUNICATING WITH EACH OF SAID RADIATING ELEMENTS; 